Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Challonge - The Ultimate Source for Tournament Brackets
Bylde - Bylde is a SaaS platform you can use to Start, Manage and Grow your groups and communities.
smash.gg - An esports platform empowering bottoms-up growth of competitive communities with value-add services...
SportEasy - SportEasy is an awesome app to communicate with your team and organize your games and practices...
Score7 - Score7 is a free tool that allows you to generate the tournament schedule according to the format and the number of participants that you specify.